Cartilage is a functional tissue found in diarthrodial joints at the ends of opposing bones and participates in load transmittal and load distribution between the bone ends. In addition to load distribution, cartilage also provides a nearly frictionless surface for the opposing bones to actuate upon so that ease of joint articulation is maximized. This type of articulating or articular cartilage is known as hyaline cartilage.
Hyaline cartilage is an aneural, avascular tissue with a very low propensity to heal after being injured or diseased. Therefore, small defects that occur in articular cartilage have a tendency to grow into larger defects. Being an aneural tissue, this progression of defects from small to large often occurs without the knowledge of the patient because of the lack of pain. When the defect reaches a size or level such that the patient begins to feel discomfort, defect progression often has occurred.
The standard of care to treat such defects includes surgical debridement of the defect area, often followed by microfracture or microdrill of the subchondral bone to induce bleeding from the bone. This treatment results in a fibrocartilage scar formation within the defect initially. However, the biomechanical properties of the repair scar tissue are inferior to that of the adjacent normal articular cartilage; therefore, the repair tissue eventually wears away to expose the defect. Since the repair tissue biomechanical properties are weaker than native articular cartilage, the articular cartilage surrounding the defect area tends to become overloaded because the repair tissue is not carrying as much load as normal articular cartilage would carry in the defect area. The result often is that as time progresses a larger defect forms than was originally present during the initial surgery.
Another treatment that is sometimes used by surgeons is known as mosaicplasty. This procedure involves removing cores of cartilage and bone from the defect site and press-fit into these holes with properly sized cartilage and bone plugs from non-weight bearing areas of the patient's knee. One or more such plugs can be used at a time. This procedure is very controversial because it is dependent on the skill of the surgeon and because the use of multiple plugs results in areas of the defect that are not covered. So, the patient's body will typically fill the gaps between and around the plugs with inferior scar tissue. There is also concern surrounding the integration of the plug with the recipient site as well as concern of the donor sites healing.
Another treatment option that is employed by surgeons uses allografts from donor human knees. Allografts must be size-matched properly to restore the patient's normal kinematics and anatomy. These grafts are also press-fit into holes that have been cored into the defect area of the recipient patient. As with mosaicplasty, similar concerns are present in addition to the concern of disease transmission from the donor human.
Another treatment option that is employed by surgeons is known as the Carticel™ procedure. This procedure is a two step process that involves harvesting cartilage from a non-weight bearing area of the knee, isolating chondrocytes (cartilage producing cells) from the tissue, and expanding (or culturing) these cells to acquire a large concentration of cells. After about 3 or 4 weeks, the patient returns to the hospital for the second step of the procedure which is the implantation stage. During this portion of the procedure, the defect area is carefully debrided, taking care to remove all of the cartilage from the defect and to not perforate or compromise the subchondral bone. Periosteum is harvested from the patient's tibia typically and sutured over the defect, leaving a small portion unsutured so that the expanded cells can be injected into the covered defect site. After the cells ale carefully injected into the defect site, the periosteum is completely sutured and the edges of the periosteal flap are sealed with fibrin glue.
Another type of cartilage that is found within joints is known as fibrocartilage. Fibrocartilage can be present intra-articularly in the form of a disc (spine, ternporo-mandibular joint), meniscus (knee), labrum (shoulder, hip), etc. . . . In the knee, the meniscus is a semi-lunar, wedge shaped tissue that sits on top of the tibia and articulates with the tibia and femur during gait activities. It acts as a shock absorber between the femur and tibia and distributes the compressive and shear loads from the curved condyles of the femur to the relatively flat plateau of the tibia. Similar to articular cartilage, much of the meniscus is avascular and aneural. However, the meniscus has three zones: red zone, red/white zone, and white zone. The red zone refers to approximately the outer peripheral third of the meniscus. This zone is rich in blood supply. The white zone can be found in the approximate inner peripheral third of the meniscus and is void of blood supply, and the red/white zone can be found in the approximate middle third and has some blood supply.
Injuries and pathology occur in the meniscus that manifest themselves in the forms of tears and degeneration. Various types and degrees of tears can and do occur often as a result of some twisting action in the knee or as a result of repetitive impact over time. Meniscus degeneration can also occur as a result of aging so that soft places develop in the tissue such that even common activities such as squatting can cause meniscal tears.
Common surgical procedures for treating meniscal damage include repairing the tears and complete or partial meniscectomies. Repairing the tear is commonly performed when the tear is a longitudinal vertical tear in the vascular (or red) zone of the meniscus. The tear is stabilized with suture or some other repair device such that the relative motion of the tear faces is minimized or eliminated during load bearing. Many devices and surgical procedures exist for repairing meniscal tears by approximating the faces of the meniscal tear. Examples of such devices and procedures are disclosed in the following U.S. Pat. Nos. 6,319,271; 6,306,159; 6,306,156; 6,293,961; 6,156,044; 6,152,935; 6,056,778; 5,993,475; 5,980,524; 5,702,462; 5,569,252; 5,374,268; 5,320,633; and 4,873,976. Meniscectomies involve the surgical removal of part or all of the meniscus. Such procedures have commonly been performed in the case of “unrepairable” or complex tears such as radial tears, horizontal tears, vertical longitudinal tears outside the vascular zone, complex tears, defibrillation, and/or degeneration. Meniscectomies typically provide immediate pain relief and restoration of knee function to the patient; however, with the absence of the meniscus, the long term effect on the knee can be cartilage wear on the condylar or tibial plateau surfaces and the eventual development of an arthritic condition such as osteoarthritis.
Other types of soft tissue that are commonly repaired by surgeons are ligaments and tendons. These soft tissues are typically attached to bone and must sometimes be reattached to bone if they are injured or become degenerative. Also, these tissues must sometimes be reattached to soft tissue if the injury or degeneration is mid-substance (i.e. occurs within the soft tissue . . . not at the bone attachment site). Common surgical procedures to repair these types of injuries include attaching soft tissue to bone with suture that is held in holes that are created through the bone (i.e. bone tunnels) or with suture that is attached to suture anchors. Common surgical procedures that are used to attach soft tissue to soft tissue include suturing, stapling, adhesives, suturing through scaffolds or reinforcement meshes.